We use JPlayer here at Senzari (http://senzari.com/) and it's been a blast to use, very easy to skin and supports fallbacks (HTML5, Flash) for every supported file format.

My only issue with it is the progress bar integration with the flash player.

We reskinned and moved every single element of it: http://cl.ly/2s323p2a1a3D3I1f1H44